Bert Coules wrote:
Chris,

Thank you for the courteous replies.

If the head of the screw *isn't* larger than the O/D of the plug then,
to my mind, the plug is *way* too large for the screw. As I keep
repeating I use 3.5 and 4mm screws in yellow plugs which go in 4mm
diameter holes in the wall. Why use anything larger?

In the case of socket boxes I'd say that the thinking behind wanting to use
a larger plug is psychological: the fixing has to hold against what seems to
be a considerable force frequently exerted against it, when plugs are
removed from sockets. What's more, that force is in the exact direction
which could pull the plug from the wall - not like, say, a wall unit or a
picture, where the force is at ninety degrees.

Given all that, those 4mm yellow plugs just seem somewhat flimsy.

Well you certainly can't pull my yellow plugs out.

What is more important to my mind is how tight the screw is in the
plug. As long as the plug is a snug fit in the hole in the wall (I
like to have to just tap the plugs in gently with a small hammer or
the handle of the screwdriver) and the screw is the right size for the
plug then it's going to be tight whether it's a 4mm screw in a yellow
plug or a 5mm screw in a red plug. Given that it's tight the
difference in grip between a yellow and a red one will be quite small
I would have thought.

--
Chris Green